Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally include one or more active layers of semiconductor material sandwiched between oppositely doped layers. When bias is applied across doped layers, holes and electrons are injected into one or more active layers where they recombine to generate light that is emitted from the device. Laser diodes are solid state emitters that operate according to similar principles.
Solid state light sources may be utilized to provide colored (e.g., non-white) or white LED light (e.g., perceived as being white or near-white). White solid state emitters have been investigated as potential replacements for white incandescent lamps. A representative example of a white LED lamp includes a package of a blue LED chip (e.g., made of InGaN and/or GaN) coated with a phosphor (typically YAG:Ce) that absorbs at least a portion of the blue light and re-emits yellow light, with the combined yellow and blue emissions providing light that is perceived as white or near-white in character. If the combined yellow and blue light is perceived as yellow or green, it can be referred to as ‘blue shifted yellow’ (“BSY”) light or ‘blue shifted green’ (“BSG”) light. Addition of red spectral output from a solid state emitter or lumiphoric material (e.g., phosphor) may be used to increase the warmth of the white light. As an alternative to phosphor-based white LEDs, combined emission of red, blue, and green solid state emitters and/or lumiphors may also be perceived as white or near-white in character. Another approach for producing white light is to stimulate phosphors or dyes of multiple colors with a violet or ultraviolet LED source. A solid state lighting device may include, for example, at least one organic or inorganic light emitting diode and/or laser.
Many modern lighting applications require high power solid state emitters to provide a desired level of brightness. Emissions from high power LEDs are often transmitted through a diffuser to create light of a more diffuse and pleasing character. High power LEDs can draw large currents, thereby generating significant amounts of heat that must be dissipated. Heat dissipating elements such as heatsinks are commonly provided in thermal communication with high intensity LEDs, since it is necessary to prevent a LED from operating at an unduly high junction temperature in order to increase reliability and prolong service life of the LED. Aluminum is commonly employed as a heatsink material, owing to its reasonable cost, high thermal conductivity, corrosion resistance, and relative ease of fabrication. Aluminum heatsinks for solid state lighting devices are commonly formed in various shapes by casting, extrusion, and/or machining techniques.
It would be desirable to provide a LED light bulb capable of replacing an incandescent bulb without sacrificing light output characteristics, but various limitations have hindered widespread implementation of LED light bulbs. One limitation that has limited widespread implementation of LED light bulbs includes fabrication cost, since assembly of numerous portions of conventional LED light bulbs typically entails assembly by hand—such as to make mechanical, electrical, and thermal (heat transfer) connections. Another limitation associated with conventional LED light bulbs includes limited directional light output. That is, in the context of a conventional high-output LED light bulb, at least a portion of a heatsink is arranged between the base and globe (or cover) portions of the bulb, with the globe or cover typically serving to protect the LED(s) and diffuse light emitted therefrom. Unfortunately, a heatsink of sufficient size to dissipate the quantity of heat generated by the LED(s) tends to block output of light proximate to the base of the bulb. When such a bulb is placed pointing upward in a table lamp, the resulting low intensity of light output in an area below the bulb and shadows are not pleasing to many users.
It would be desirable to reduce or eliminate hand assembly steps, and therefore reduce cost, for fabricating LED light bulbs. It would also be desirable to enhance heat dissipation in LED light bulbs in order to reduce the need for bulky external heatsinks, and therefore provide light output over a greater range of directions, including enhanced output proximate to the base of a LED light bulb. It would also be desirable to promote lower LED junction temperatures in order to prolong LED operating life.